In practice chemical decapsulation processes are used for decapsulating crustacean eggs and especially for decapsulating Artemia cysts. The importance of decapsulating Artemia cysts when used as food in aquaculture has already been described by Sorgeloos et al. in the article “Decapsulation of Artemia cysts: a simple technique for the improvement of the use of brine shrimp in aquaculture” in Aquaculture, 12 (1977) 311-315 and recently revised by Dhont and Sorgeloos in “Applications of Artemia ” in: Artemia, basic and applied biology, edited by Abatzopoulos et al. (2002) 251-277. The main advantages to use decapsulated cysts of the brine shrimp Artemia is the achieved disinfection and that no separation of the nauplii from the hatching debris is required. Moreover, decapsulated non-hatching cysts can be used for direct ingestion and digestion by marine fish and crustacean larvae which means a valorisation of an otherwise inferior product. Consequently, the decapsulated cysts do not necessarily have to be viable. However, since the Artemia nauplii, which hatch out of the Artemia cysts, are commonly used as live food organisms in aquaculture, more particularly as live food for the early larval stages of marine fish and shrimp, the decapsulation process is preferably carried out under conditions which are non-lethal for the cysts.
In practice, the Artemia nauplii as live food are not marketed as such but as Artemia cysts. Hatching of cysts is done by incubating them in a hatching medium for an incubation period that is typically shorter than 24 hours so that everyday a new supply of free swimming nauplii can be produced using the same hatching infrastructure.
To harvest the daily needed portion of free-swimming nauplii, they first need to be separated from empty shells and unhatched cysts. Several separating techniques exist whereby the empty shells are floating at the surface meanwhile the swimming nauplii are siphoned at the bottom from the tank. However, some batches of Artemia can hardly be separated. The unhatched cysts and empty shells often cause deleterious effects when they are ingested by the predator. They are not digested and may cause obstruction of the gut. Moreover, as cyst shells are loaded with bacteria, infections may occur in fish or crustacean cultures after the addition of a mixture of nauplii and cysts (or shells).
In the known decapsulation processes, the hard dark brown external layer of the cyst, the chorion or tertiary envelope, is removed by short-term exposure of the hydrated cysts to a hypochlorite solution. The chorion can be oxidised because it is comprised of lipoproteins. However, the embryonic cuticle beneath is chitinous and nonreactive in hypochlorite solutions so that the viability of the enclosed embryo is unaffected when the decapsulation process is carried out correctly.
The known decapsulation processes of brine shrimp cysts typically involve four steps (see the above mentioned article of Sorgeloos et al., U.S. Pat. No. 4,163,064 and Van Stappen, “Use of cysts” in Manual on the production and use of live food for aquaculture, edited by Lavens and Sorgeloos (1996) 107-136″); (i) hydration of cysts in seawater or freshwater; (ii) oxidation in a strong hypochlorite solution and NAOH; (iii) stopping the oxidation reaction at a predetermined time by dilution with water and (iv) thorough rinsing to remove debris and traces of chemicals after which the denuded cysts either can be transferred to a saturated saline solution to be packed in a brine for future use or they can be fed to cultured animals directly.
Advantages of a chemical decapsulating process are the decreased labour costs by eliminating time consuming processes of separating newly-hatched brine shrimp from unhatched and empty shells, the fact that denuded cysts are 100% edible even in their unhatched state and that it provides a product which tend to hatch better with a higher nutritional value. Moreover, through the elimination of the outer shell, a source of bacterial contamination is removed.
A drawback of the known decapsulation process is, however, that it is impractical to implement on a large scale due to the pollution caused by the chemicals incorporated in the process and the environmental concerns that are raised for the disposal of such chemicals. Due to the use of hypochlorite, the wastewater contains high levels of toxic products, which are difficult to purify. Tests we performed have shown that the process water contains high levels of AOX (Absorbable Organic Halogen compounds) and TOX (Total Organic Halogen compounds), which nowadays restrict the process to be carried out on a big scale due to environmental concerns for the disposal of such chemicals.
It would therefore be advantageous to provide a new chemical decapsulation process wherein the use of a hypochlorite solution can be avoided.